The present invention is related to a multiple access communication network.
A The invention is also related to a transmitter, a receiver, a transmission method and a signal.
Such a transmission system is known from the ETSI standard ETS 300 175-2, Radio Equipment and Systems (RES); Digital European Cordless Telecommunications (DECT) Common Interface, Part 2: Physical layer, section 4: Physical layer services pp. 14-23.
The DECT standard describes a time domain multiple access communication system in which a plurality of secondary stations can transmit data to a primary station using time slots-with a length of 480 bits. Of these 480 bits, 32 bits are used for synchronisation, and 64 bits are used for control purposes. Furthermore, 60 guard bits are used to prevent collisions between packets from different secondary stations due to differing transmission delays between different secondary stations and the primary station. Consequently 324 bits are available for transmitting payload. If an ATM cell of 53 bytes (=424 bits) should be transmitted, the available 324 bits are insufficient.
It is also possible to use a double slot having 800 bits available for payload transmission. Transmitting an ATM cell in such a double slot uses 424 bits, leaving 376 bits unused. This results in a very inefficient use of the available bandwidth.
The object of the present invention is to provide a communication network according to the preamble in which 53 bytes ATM cell can be transmitted in an efficient way.
To achieve said objective, the present invention is characterized in that the secondary stations comprise packet assembling means for assembling extended length packets comprising two 53 bytes ATM cells, and in that the secondary stations comprise delay compensation means for adjusting their transmission instants to compensate delay differences between different secondary stations and the primary station.
The present invention is based on the recognition that it would be possible to transmit two ATM cells in a double slot without altering the number of overhead bits if the guard space could be reduced to not more than 12 bits. In order to be able to reduce the amount a guard space, delay compensation means should be used.
These delay compensation means are arranged for choosing the instant on which the symbols are transmitted to the primary station in such a way that these symbols arrive at the primary station exactly at the beginning of a timeslot. If the secondary stations use such delay compensation means, the guard time can be substantially reduced, making it possible that two ATM cells can be transmitted in a double slot.
An embodiment of the invention is characterized in that the extended packet comprises a 32 bits synchronization field, a 64 bits control field and a 4 bit crc field.
In this way a packet is obtained having the same construction as a DECT P80 field, except the length of the payload area. This has the advantage that slightly modified DECT equipment can be used in the primary and the secondary stations.